1. Field of the Invention
The invention relates to a probe for attachment to land and marine animals which is capable of detecting and measuring light, and more particularly to such a probe which is wavelength-selective and which detects light from essentially all directions so that the measurements are not dependent upon any particular orientation of the probe.
2. Description of Related Art
Attempts have been made to determine and study the migration and/or wandering patterns of certain forms of marine life, particularly species of fish which have been threatened with extinction due to, for example, intense fishing pressure. For example, due to their high value in the far east marketplace, blue fin tuna have been particularly victimized in recent years to the point where the population of this tuna has dropped by a factor of about ten.
One way which has been used to learn some information about the movements of fish is by tagging the fish with markers such as color-coded visible implant tags. Such tags allow for the identification of fish, so that upon recapture of a particular fish, it can be learned to what location that fish travelled.
Although the tagging method provides information as to the ultimate location of a particular fish upon recapture, this method does not yield any information as to the route by which the fish moved from a point A to a point B. It would be desirable to learn more information as to the route which the fish took in its journey for the purpose of determining, for example, whether the particular fish migrates or merely wanders.
In an attempt to learn more information about the journey of a fish from one location to another, photo detecting devices and thermistors have been developed for attachment to the fish. Upon recapture of the fish, the light intensity information measured by the photo detector and recorded along with time-of-day information by some means in the device can be interpreted to learn the geographic longitude of the fish each day by noting the time of sunrise and sunset and performing standard calculations of celestial navigation. Temperature measurements taken by the thermistor and also recorded can be compared to known reference values of ocean temperature to yield information about the latitude of the fish during its travels.
One major problem encountered with the use of such photo detecting devices is that the measurement of the ambient light intensity may depend on the orientation of the detector because it is not held in a fixed orientation with respect to both the water surface and the direction of the sun. This can result in data which is not useful because it will not accurately reflect the true location of the fish. Therefore, it would be desirable for the photo detector to have a very broad light acceptance angle, or, ideally, that it be omnidirectional so that the measurement of ambient light intensity does not depend on the instrument's orientation.
Another problem encountered is that when the light measurement is made at some depth in the ocean some light is absorbed by the intervening water. The values measured must be corrected to take into account this absorption.
Yet another problem encountered with the use of light detecting devices is that ocean water is a conductive fluid which readily promotes corrosion of exposed metallic surfaces. In addition, sea water is known to promote the fouling of exposed photo detector surfaces.
Photo detectors with an optical filter which passes only a narrow range of wavelengths and with a diffuser which broadens its acceptance angle are known. In addition, it is known to arrange multiple sensors in a single probe so that only nonmetallic and fouling-resistant surfaces are exposed to the sea water. However, heretofore, it has not been possible to combine these known structures in the form of a thin, flexible probe which can extend through the skin of the fish into the surrounding sea water. In particular, a major problem in creating such a device is the fact that an effective diffuser is ordinarily large compared to the detector surface itself. Therefore, it would be an improvement in the art to integrate all of the above-referenced functions in a thin, flexible structure.